From s-clemens@wildmail.com Mon Jul 9 13:03:25 2001 Received: from mxu1.u.washington.edu (mxu1.u.washington.edu [140.142.32.8]) by lists.u.washington.edu (8.11.2+UW01.01/8.11.2+UW01.04) with ESMTP id f69K3L078364 for ; Mon, 9 Jul 2001 13:03:21 -0700 Received: from C9Mailgw04.prontomail.com ([216.163.188.10]) by mxu1.u.washington.edu (8.11.2+UW01.01/8.11.2+UW01.04) with ESMTP id f69K3LF29604 for ; Mon, 9 Jul 2001 13:03:21 -0700 Received: from c9web103 (216.163.188.10) by C9Mailgw04.prontomail.com (NPlex 5.5.029) id 3B3CA0170019C2D9 for waphgis@u.washington.edu; Mon, 9 Jul 2001 12:58:21 -0700 X-Version: caremail 6.3.3401.0 From: "Susan Clemens" Message-Id: <8E2A619E79475D1168D50005B80E61C3@s-clemens.wildmail.com> Date: Mon, 9 Jul 2001 13:03:30 -0700 X-Priority: Normal Content-Type: text/plain; charset=iso-8859-1 To: waphgis@u.washington.edu Subject: Re: RE: Zip Codes, ZCTA and areal interpolation. X-Mailer: Web Based Pronto Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable I have been skeptical of zip codes and/or ZCTA for some time now. Unfor= tunately, I am usually analyzing data collected by another agency so don't have the option of requesting more specific geographic = information. Often a zip code is all that is collected or all that can be released due to patient confidentiality issues. I agree with the observation that zip codes are not consistent through = time. As I understand it, perimeter changes are the norm when designating new zip codes. Also, zip + 4 numbers change more frequentl= y than zip code perimeters and often have more to do with postal carrier staffing and routes vs population. Lastly, the ZCTA for= the 1990 Census were developed using a different methodology than the 2000 ZCTA. Even if you are lucky enough to be in an area with= no new zip codes you cannot compare 1990 and 2000 ZCTA data. So, where does this leave us? Is commercial zip code level data any mo= re reliable that the ZCTA? Is any zip code level analysis for health valid given the constraints mentioned? Susan Clemens Humboldt Co Dept of Public Health ---- Begin Original Message ---- From: fpb01@health.state.ny.us Sent: Thu, 5 Jul 2001 15:44:38 -0400 To: waphgis@u.washington.edu Subject: RE: Zip Codes, ZCTA and areal interpolation. I believe that ZCTAs were created for the exact purposes given in Richa= rd's original posting: to provide an easier way to deal with the mass of dat= a that is geocoded to zip code only, and to provide a standard (and free)= base map on which to map this data. ZCTAs are probably good enough for many purposes, such as marketing applications. They should also be good enough for certain kinds of proportional analysis. For example, you can probably safely compare a variable such as % smoking from a zip code-based survey with % complete= d high school from ZCTA. When it comes to using ZCTAs for calcuating incidence and mortality rates, though, I am pessimistic. Frank Boscoe NYS Department of Health "Richard Hoskins" @u.washington.edu on 07/05/2001 03:12:24 PM Please respond to waphgis@u.washington.edu Sent by: =A0WAPHGIS-owner@u.washington.edu To: =A0 cc: Subject: =A0RE: Zip Codes, ZCTA and areal interpolation. Frank: =A0What was the purpose of the census bureau's developing the ZC= TAs? Dick H -----Original Message----- From: WAPHGIS-owner@u.washington.edu [mailto:WAPHGIS-owner@u.washington.edu]On Behalf Of fpb01@health.state.ny.us Sent: Thursday, July 05, 2001 12:00 PM To: waphgis@u.washington.edu Subject: Re: Zip Codes, ZCTA and areal interpolation. I believe that conversion from Zip Codes to ZCTAs is, unfortunately, mo= re than just an areal interpolation problem. The two entities are not the = same thing - they differ along the edges. On a road that forms the boundary = of a zip code, both sides of the road may be in the same Zip Code. This is reasonable and facilitates the delivery of the mail. But the two sides = of the road will be in different census blocks and hence different ZCTAs (since ZCTAs are built from census blocks). =A0In heavily populated are= as, the distinction is almost negligible, but not in rural areas. In fact, = the census produced a graph which shows that zip code-ZCTA agreement is alm= ost perfect in zip codes with more than 15,000 addresses, but under 80% whe= re there were fewer than 250 addresses. In terms of health mapping, if a nursing home or hospital or other spec= ial type of address falls on a zip boundary, its entire caseload could be assigned to the wrong ZCTA, resulting in substantial error even in a heavily populated area. Frank Boscoe NYS Department of Health ---- End Original Message ---- Care2 make the world greener! http://www.care2.com - Get your Free e-mail account that helps save Wil= dlife! .